LONDON — Dozens of people were arrested outside a London courthouse on Thursday after expressing support for Palestine Action, a protest group that has been banned as a terrorist organization by the British government. Police detained protesters who gathered outside Westminster Magistrates’ Court shouting “I oppose genocide, I support Palestine Action,” as onlookers shouted “Shame!” More than 3,000 people have been arrested for actions as simple as holding signs declaring “I support Palestine Action” since the group was outlawed. On Thursday the Supreme Court said Palestine Action founder Huda Ammori can take the case to the country’s top judges. All cases of people charged with breaching the ban have been put on hold until the Supreme Court rules, court officials said.